Organic electroluminescent devices are also known as organic light emitting diodes (OLEDs). The OLED luminescent principle applies a voltage to organic molecular material or polymer material, and the device luminesces. Due to self emission characteristics of the OLED, dot matrix type displays have been produced that exhibit light weight, slim profile, high contrast, low power consumption, high resolution, fast response time, no need for backlighting, and full viewing angle. Possible display parameters range from 4 mm microdisplay to 100 inch outdoor billboards and make it a preferred type of flat panel display (FPD). Referring to FIG. 1, an organic electroluminescent device is operated by a switch transistor 102, and a driving transistor 104 coupled to a power line Vp. Organic electroluminescent devices 106 typically, however, suffer from non-uniform brightness between pixels. Specifically, brightness decays when the organic electroluminescent device 106 is operated for a long period of time.